It was seen as a good move at the time, and even better now that Daniel Theis is out for the season after suffering a left meniscus tear in Boston’s 99-97 loss to Indiana on Sunday.

Many players, including Terry Rozier whose locker stall is next to Theis, said he didn’t find out about the injury until he arrived for practice on Monday.

“It sucks because that's my locker room guy. We're right next to each other at the arena and here so you know, we built a relationship,” Rozier said. “It's just tough to see it - not come to an end - obviously he's still going to be able to play basketball, but just with the season almost coming to an end, and then that happens, so it just sucks to see it. Great guy.”

But the injury to Theis reaffirms Boston deciding to acquire Monroe following him coming to terms on a buyout with the Phoenix Suns, rather than making a trade with the Memphis Grizzlies or the Los Angeles Clippers who wanted Boston to include a first round pick for any deal involving Grizzlies wing Tyreke Evans or Clippers guard Lou Williams who was a borderline all-star this season.

“One of the reasons why we wanted to sign Greg,” said Celtics coach Brad Stevens, “was because you never know what can happen with your depth inside.”

Prior to signing Monroe, the 6-10 Daniel Theis was the team’s only player off the bench they could turn to and get size.

But with Theis out, that depth won’t be nearly the same.

While Monroe is a much better inside, on-the-block scorer than Theis, Theis’ energy and hustle will be sorely missed.

“Just incredible reliability and energy,” said Celtics head coach Brad Stevens. “I appreciate the way he approached every day. And he’ll approach rehab the same way. You really feel for him. He was a guy that came in … he came in knowing he could play, but not even expecting him to have the kind of season he had. And he didn’t change that when we brought Greg in. We mixed up minutes here and there. He just kept being who he is. We’re going to miss him on the court. But he’ll have a full recovery and get back better than ever when he steps back on the court.”

There’s no telling what Theis’ absence will mean for Monroe who has appeared in 11 games for the Celtics, averaging 7.8 points and 5.0 rebounds while shooting 54 percent from the field.

But when he signed on with the Celtics over his hometown New Orleans Pelicans, it was an opportunity like the one before him now that Monroe has been waiting for patiently.

“I just try to be prepared for every game,” Monroe told NBC Sports Boston. “My perspective, my mentality, I try to go into every game with the same focus.”

"Even though he was scoring the basketball, he didn't try to rush or he didn't press," said Cavs coach Tyronn Lue. "He just played within the game and took his shots when they were there. He played like a veteran tonight. He didn't try to force anything and just took what the defense gave him."

And on a night when the Celtics had stretches of ineffective play at both ends of the floor, they absolutely needed Tatum to deliver a special performance such as the one we saw in Game 5.

“I just thought he had a really good game,” said Celtics coach Brad Stevens. “Again, these guys were anxious to play. Everybody is anxious after you get beat. But I think Jayson was especially anxious after Game 4.”

Tatum has been Boston’s leading scorer in the postseason but has struggled for stretches in this series dealing with Cleveland’s more physical brand of basketball that has made scoring a lot tougher for him.

When asked about the physicality between the regular season versus the playoffs, Tatum replied, “It’s like night and day.

He added, “Guys are going to be physical, especially with me being the young guy. That tends to happen a lot. It’s just guys trying to be stronger and bigger than me, so they’re just trying to be more physical.”

But Tatum has shown he can handle the physical play and in turn, dish it out defensively where his length allowed him to contest most of the shots taken by whoever he was defending, in addition to giving him a shot at getting into passing lanes to create turnovers or at a minimum, disrupt Cleveland’s offense.

One of Tatum’s most outspoken supporters on the Celtics roster has been Al Horford.

“That was encouraging to see Jayson really just taking on the challenge, really playing well on offense, playing well on defense,” Horford said. “Just very poised for most of the night. I was just very happy to see him have such a good game.”

But it didn’t come as a surprise, not with the kind of season Tatum has had for the Celtics.

However, if Tatum seemed a bit more aggressive offensively than usual, it might have had something to do with a chat he had with Stevens.

“I knew I was going to play a little bit more in the first quarter, just to look to be more aggressive,” Tatum said. “Coach trusts that I’m going to make the right play …”

As he should.

Because the track record of success for Tatum in this his first NBA season is undeniable.

The youth movement that has engulfed this franchise has been led by the play of a number of young players, with Tatum’s play and potential as a star in this league being one of the primary driving forces that has done the seemingly unthinkable – positioned the Celtics to be within one victory of a trip to the NBA Finals.

“I can’t say it enough,” Tatum said. “We’re one win away from going to the Finals, especially after everything we’ve been through.”

There was Gordon Hayward’s season-ending injury just five minutes into the season, followed by a slew of other basketball-related adversity that included not having Kyrie Irving for the entire postseason.

But those injuries created opportunities for young players like Tatum.

And to his credit, no one has made the most of that opportunity for an enhanced role, better than Tatum.

But the focus now for Tatum and the Celtics is to do the seemingly unheard of – send LeBron James home for the summer.

“It’s tough to finish out games,” Tatum said. “You’ve got to give it your all until there are zero seconds left on the clock.”

1:22 - Mike Gorman and Tommy Heinsohn break down the Celtics big Game 5 win over the Cavaliers, and discuss what they think the keys are for the Celtics to get a win on the road and end the series in game 6.

6:03 - The Celtics were able to hold LeBron James to 26 points in game 5, Brian Scalabrine and Kyle Draper break down what they saw the Celtics do to slow down LeBron, and how they can build off that to finish the series.